Testing system



. Oct. 2, 1923.

OHMS D.C. RESISTANCE Miken/0r.'-

#afl/e] Hakbar, I by Any Patented @et 2, i923.

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HARVEY FLETCHER, or` NEW Yonai, NY., yassrerNoE To WEsTEEN ELECTRIC corr-` PANE', INcoEroaaTEn, or NEW Yoan, N. Y., AooEPoEE'TroN or NEW YoEir. Y

TESTING SYSTEM.

Application led ctober 19, 1922. ASerial No. 595,503.

To all whom t may concern.:

Be it known that I, HARvEX Fnnfrorrniz, a citizen of the United States, residing at New York, in the county of New York, State of New York, have invented certain newV and useful improvements in Testing Systems, of

which the following is arfull, clear, concise, and exact description; i f A This invention relates to systems for determining theefticiency of' telephone apparatus andfparticularly to a'systemrfor testing the eiliciencyof subscribers transmitters.` i 1, l

The object of this invention infgeneral is to provide ajconvenient and eircient system for readily determining the efficiency of a subscribers transmitter.' A

In accordance with the' general features of this invention,'a subscribers transmitter v his invention lis particularly applicable to the testing of subscribers"-transmitters which are in service ata way station but is not limited to this application.

Referring to the drawings, Fig. l'shows schematically a subscribers loop andthe connected apparatus used in making a test. Fig. 2 shows characteristiccurves giving the relation between the Aalternating voltage generated by a certain type oft'ransmitter and the effective direct current resistance of 'the transmitter, when the transmitter is subjected tovarious degreesl of agitation.'

In order to make a test, twom'en are required, one to make thecircuit changes and adjustments at the substation, and the other to make them at the central office.A The subscribers .transmitter T, is replaced' by resistance l which has a value egual tofthc average direct current resistance of a transf mitter when subjectedV to standard agitation. Y

Resistance 2'is then adjusted until meter A,

Vshows that'battery Sis ycausing thev desired .amount of direct current, e. g.\90 milliamperes, to How throughwinding .4, line conductor 5, resistance il, choke coil 6, line f conductor?, and winding 8. The direct cur rent is thencaused'to flow through transmitter T by substituting'the transmitter for resistance -1`. lf desired, thesubstitution of resistance 1 for transmitter T, and vice;

versa, may be accomplished by meansvofa switch 9.l

Resistance 10 isadjusted until alternating` current voltmeter ,V shows that a predetermined standard value of alternating voltage is being applied to theV line by source ll.v

Source ll is preferably a generatorV which delivers a voltagehaving'a frequency ampli-V tude characteristic .corresponding vapproximately tothe frequency amplitude charac- Y teristicv of speech. The alternating current passes overr the line and energizes standard receiver R,Vwhich is connected inv bridge of the line by means of a transformer 12`hav'- ing primary winding 13 and secondary lwinding 14,. A choke coil' prevents this receiverenergizing circuit from" passing through transmitter T and condenser 15,. lt is preferable that transformer@ have suchl a high impedance, of the windingl-B, that the receiver R will always give the same output for a definite voltage indicated by meterV regardless of the length of thesub-V scribers loop.

Receiver. R .which is Vnow giving a stand! ard output is acoustically coupled to transmitter T thereby subjecting the transmitter to standard agitation. 'If desired,a tube 16A may be employed to enclose an aircolumn between the transmitter and the receive-r. Due to the 'agitatiomtransmitt'er TA i .suffersanincrease in the eective value of its direct current resistancethereby causingV a4 decrease in .the direct current which y is'indicated by meter A1. This decreasein current is a vfunction ofthe increase inresistance ofy the transmitter rand hence 'function of the alternating voltagegenerated by the'transmi'tter, as is 'shown byY Fig. 2.; or the example chosen, curve trof Fig.

2 is the one oi interest since it shows .thev

relation between the alternating voltage generated by a certain type ot' transmitter and the eliective value of thedirect current resistance of thetransmitter, for the casev YWhere the steady Y state direct Acurrent irou'gh the transmitter isY 90 -milliainperesL Meter A1 must be of rel ativcly high range, Vwhich forthe eXa-mple chosen, would mean a full scale deliection of at lcast 90 milli- Vainperes. VSuch a meter may not sufiicientlyv accurately indicate changes in the value of direct current caused' by the increase in re.- sistance oi: transmitter VT. To obtainmore accurate readings. in current change, a seci ond ineterA2` of relatively lonT range, e. g.,

15 milliamperesfull scale deflection, may be inserted in series with meter A, and set back Y z'ioby means of a shunt connected battcry'l? in'series With a resistance 18, so as to render meter A21-operative to indicate changes inV a current of the order of 90 milliamperes.

Wvhen this arrangement' is used, the trans- .l mitterV direct current is adjusted by shifting Y resistance 2 until meter-,Y indicates the de-4 sired standard jfvalue such as` V90 milli-V ainperes. VThen resistance 18"is adjusted to produce ja Ydesired standard settingoffmeter 36 Age. g., l() vmillia-mperes. Upon ajr ,i*tati'on of"the,transi'nitten meter A2 willV taire rup )a change Yin deflection which is a function ot the change in resistance of transmitter T fand hence a function of. the alternating volt-v r age generatedby the transmitter. It de-Y sired, this meter may be calibrated to read directly the Valt'ernat-ing voltage vgenerated Yby the transmitter, and by taking the ratio of this voltage to thelrnown voltage which a standardA transmitter generatesunder like conditions, a measure of the efficiency of theV subscriberstransmitter T is obtained. This ratio may be converted into miles of standard cable or other transmission'unit, as is V"Well understood'in the art. Y

'lf o] is the voltage.generatedbi7 thev sub? i scriberstransmitter and o2 is the Vknown voltage generated by a standard,transmitter under .like conditions, it is apparent that ratiov @l is equalV toa constant times i), for

Y anyV particular ltypeV oi" transmitter Which is being tested ;i and hence,'ir` desired, meter A, may be calibrated to tread the eiiiciency have been provided whereby the eiiiciencyV ofthe subscribers transmitterT` directly in terms 'oi miles of standard cable or other Y convenient transmission unit.

in the specification, mention is made of values of current, but itis to be understood that these values are merely illustrative, and

that*values'ofcurrent voltage and resistance j .should be chosen which are the inostsuit` able for the apparatus involved. j

ltjis seen that a method and apparatus Voi" a subscribers transmitter canbe readily Y determined Without the transmit-ter being .ceiver, means for measuring the alternating 'Y Vtransmission line to said'ltransmitter, means ,removed from the subscribers station or a ground return being used between the subj scribers station and the central office.

The invention'claimed is: f Y

l.Y The method of determining the etliciency or' a subscribers.transmitter which" coniprises subjecting the transmitter to a definite agitation, indirectly measuring the alternating voltage generated by said'transmitter by Y means of a device responsive to changeV in direct current through the transmitter, and

Vcomparing said voltage to the voltage generytransmitter Yand comparing said voltage ton thejvoltage vgenerated by a standard'transmitter when subjected toA tliersaine conditions.Y .i

3. In a system for measuring the eiiiciency of a Vtelephone transmitter, a transmission line across Which the transmitter is bridged, a receiver in brridge o'l' the transmission line, means for sending direct current overthe transmission line to u saidv trans-V mitter, means for sending -alternating current overthe transmissionline to energize said receiver,- andmeans for measuring the Y voltage which Acausessaid alternating Vcur- Y i rent to iow. A

' 4. ln a system for measuring the efficiency of a telephone transmitter, va transmission line across which the transmitter is bridged,

a receiver in bridge of the transmission j line, means for sending direct current .over` the `transmission line to l'said transmitter, means for sending Yalternating current Vover the transmission line to venergize said re- 115 voltage Which'causes said alternating current tonflow, `and means" for substantially excluding saidalternating current from Asaid transmitter.A Y .j n Y Y.

5. In a system for measuring the efficiency 12o oit-a telephone transmitter, at'i'ansmission line across'which the transmitter is bridged,

a receiverinibridge-of the transmission line, means for sending direct .current over the '125 for sending alternating current over :the

transmission line to energize "said receiver,

said alternating current havingvenergy-trequency spectrum .corresponding approniinately to voice current, and means for'V me, Y.

measuring the voltage which causes said alternating current to flow.`

6. In a system for measuring the ei'liciency of a telephone transmitter, a transmission line across Which the transmitter is bridged, a vreceiver in bridge of thev transmission line, means for sending direct current over the transmission line to said transmitter,

means for sending alternating current over the transmission line to energize said receiver, means for measuring the voltage which causes said alternating current to flow, and means responsive to changes in the direct current through said transmitter.

7. In a system for measuring the eiiciency of a telephone transmitter, a transmission line across which the transmitter is bridged, a receiver in bridge of the transmission line,

'means for sending direct current over the transmission line to said transmitter, means for sending alternating curernt over the transmission line to energize said receiver, means for measuring the voltage whichV causes said alternating current to iow, means for substantially excluding said alternating current from said transmitter, and i means responsive to changes in the direct current through said transmitter.

In Witness whereof, I hereunto subscribe my name this 17th day of'October A. D., 1922.

' HARVEY FLETCHER. 

